As the use of the Internet and the World Wide Web (“Web”) has become widespread, it is increasingly common for users to access and use various types of capabilities provided by remote computing systems over the Web, including to search for, shop for and order products (such as goods, services and/or information) that are for purchase, rent, lease, license, trade, evaluation, sampling, subscription to, etc. After a user places an order for one or more such products (e.g., via a Web merchant or other online retailer, via an electronic marketplace, etc.), the order is fulfilled, such as by providing goods that have been ordered through physical distribution channels (e.g., shipment via a governmental postal service or private common carrier) or electronically (e.g., via download over the Internet, such as for digital music or videos) as appropriate. Ordered services may similarly be provided electronically (e.g., providing email service) or physically (e.g., performing cleaning services at the purchaser's house).
In addition to such user-initiated interactions (e.g., interactions initiated by users using Web browser applications to interactively request Web pages from Web servers), software programs on remote computing systems may also interact for various purposes and in various ways. For example, there is growing use of the Web to provide so-called “Web services,” which typically involve the programmatic interaction of remote applications to exchange information via defined APIs (“application program interfaces”). Web services allow heterogeneous applications and computers to interact, and may be defined and implemented using a variety of underlying protocols and techniques. For example, some Web service implementations return data in XML (“eXtensible Markup Language”) format using HTTP (“HyperText Transport Protocol”) in response to a Web service invocation request specified as a URI (“Uniform Resource Identifier”), such as a URL (“Uniform Resource Locator”) that includes a specified operation and one or more query parameters. Such URI-based invocation requests may, for example, be based on the use of XML over HTTP (e.g., as part of the REpresentational State Transfer, or “REST”, distributed interaction model that focuses on resources). In other implementations, additional underlying protocols are used for various purposes, such as SOAP (“Simple Object Access Protocol”) for standard message exchange, WSDL (“Web Services Description Language”) for description of service invocations, and UDDI (“Universal Description, Discovery, and Integration service”) for discovery of available services. Furthermore, various other types of programmatic interaction mechanisms have been developed and used, including remote procedure call (“RPC”) protocols, various object-oriented and other architectures such as CORBA (“Common Object Request Broker Architecture”), Java RMI (“Remote Method Invocation”), JavaSpaces, Jini, JXTA, UPnP (“Universal Plug and Play”) and DCOM (“Distributed Component Object Model”), and a variety of middleware programs that connect separate applications (e.g., various EDI, or “Electronic Data Interchange,” networks).
Unfortunately, while Web services and other programmatic interaction mechanisms allow various application programs and computers to interact, such interactions are typically limited in various ways. For example, the types of information and functionality that are available to be requested using such programmatic interactions are typically restricted to very limited types of requests that the remote computer systems and applications can automatically fulfill (e.g., to provide a specified predefined group of information, such as a Web page or file, or to perform a specified database query on a specified database).